1. Field of the Invention
This invention relates to a method and a device for lifting single crystals, said device of which is installed in semiconductor single-crystal manufacturing equipment that utilizes the Czochralski(CZ) method. The method and the device are especially adaptable for lifting heavy semiconductor single crystals.
2. Description of the Related Art
Conventionally, silicon single crystal is produced by the CZ method. In the CZ method, polycrystalline silicon is deposited into a quartz crucible of a single-crystal manufacturing apparatus, then the polycrystalline silicon is heated until it melts by way of heaters disposed around the quartz crucible, subsequently a seed crystal installed within a seed holder is dipped into the melted liquid. Then, the seed holder and the quartz crucible are respectively driven to rotate in the same or opposite directions. At the same time, the seed holder is lifted to grow a single crystal of predetermined diameter and length.
In the seed crystal, dislocation will arise due to the heat shock occurring at the time of dipping it into melted liquid. In order to stop propagation of dislocation from the seed crystal to the single crystal that is to be grown, a reduced portion with diameter from 1 to 4 mm is grown beneath the seed crystal so as to release the dislocation to the surface of the reduced portion. After making certain that the propagation of dislocation has been stopped, a shoulder is formed and the single crystal is enlarged to a predetermined diameter. Then, the lifting operation is shifted to that of forming the body of the single crystal.
In recent years, following the enlargement of single crystals, the weight of an individual single crystal has increased, and the strength of the reduced portion has nearly reached its limit. To solve the problem, a necked portion with a diameter larger than that of the reduced portion is formed on the top of the shoulder when the propagation of dislocation has been stopped by way of the reduction process. It is possible to hold the single crystal by the necked portion so as to prevent breakage of the reduced portion. Alternatively, means are taken to prevent dropping of the single crystal even if the reduced portion breaks. For example, in the single-crystal lifting device disclosed in Examined Japanese Publication NO. 5-65477, 3-4 clamp arms capable of being driven to open or close are engaged with the necked portion of a single crystal so as to suspend the single crystal. In addition, in the single-crystal lifting device disclosed in Examined Japanese Publication NO.7-103000, a plurality of claws engaging with the necked portion of a single crystal are provided. The single crystal is suspended by utilizing a plurality of holding levers capable of being driven to open or to close by their ascending or descending movement and a ring used for preventing opening of the holding levers. Furthermore, in the single-crystal lifting device disclosed in Examined Japanese Publication NO.7-515, a plurality of claws retained at a predetermined angle are provided at the lower end of an engaging holder capable of being driven to ascend or descend. The claws are engaged with the necked portion of a single crystal so as to suspend the single crystal.
However, in the single-crystal lifting device disclosed in Examined Japanese Publication NO. 5-65477, the clamp arm will be driven to open when the weight of the single crystal increases, and there is the danger of dropping of the single crystal during the lifting operation. In the single-crystal lifting devices disclosed in Examined Japanese Publication NO. 7-515 and No.7-103000, there is the danger that the single crystal being lifted might convert into a polycrystal due to the mechanical shock or vibration induced in the process of clamping the single crystal. Furthermore, it is impossible to take the single crystal off from the clamping means,, once the single crystal has been clamped and installed in the main chamber. Thus, even if polycrystallization of the single crystal being lifted or dislocation has occurred, it is impossible to re-melt the single crystal.